This invention relates to a dynamo-electric machine and more particularly to an improved insulator for the armature thereof.
Rotating electrical machines have been proposed for many applications. For example they may be used as a starter motor for an internal combustion engine. In such an application, a DC electric motor is powered from a battery for starting the engine. The starter motor generally comprises a stator comprising a cylindrical yoke with a plurality of magnets circumferentially bonded to an inner surface of the yoke. An armature (rotor) having coils arranged opposite the magnets and supplied with electrical current for driving a rotating shaft of the armature forming a output shaft of the starter motor. The motor output shaft drives a crankshaft of the engine via a reduction gear, an overrunning clutch for starting the engine in a well known manner.
The magnets may be ordinary magnets obtained by magnetizing a ferrite type magnetic material. The coils are formed by winding a wire (in general, a thin wire having a diameter of 0.9 mm or less) on each of a plurality of radially arrayed magnetic pole teeth of the armature. These pole teeth have a general T-shape. At this time, the core pole teeth are covered with insulators around which the wire is wound. In order to reduce the size and to increase the power, starter motors employing high-energy neodymium type magnets instead of the ferrite type magnets has been developed. When neodymium type magnets are employed, the thickness of the magnets can be decreased and the output of the motor can be enhanced. When such high-energy neodymium magnets are employed, the coils are formed using a wire having a diameter of about 1 mm or greater so that a current corresponding to the energy of the magnets can flow.
This thick wire has a high rigidity, so that it requires a large tensile force to wind the wire around a magnetic pole tooth to form a coil. Thus, a large pressing force corresponding to the tensile force is exerted on coil end surfaces of the magnetic pole tooth. A method and apparatus for forming such windings is disclosed in the application entitled xe2x80x9cWINDING METHOD AND DEVICE FOR AN ARMATURE FOR ROTARY ELECTRIC MACHINESxe2x80x9d, Ser. No. 10/064,923, filed concurrently herewith by the assignee hereof, based upon Japanese Application Serial Number 2001-271207, Filed Sep. 7, 2001.
Although the method and apparatus described in that copending application is very effective in providing the coil winding, still further improvements can be made. For example, a large stress is applied to edges of the coil end surfaces, namely, edges of the magnetic pole tooth, against which the wire is bent and pressed. This problem can be particularly difficult in connection with the insulating material around which the wire is coiled. This may be understood best by reference to FIGS. 1 through 4. As noted below, these figures are, respectively, a top plan view of the one half of insulating material, a cross section taken along the line 2xe2x80x942 of FIG. 1, a bottom plan view of the insulator half and a cross sectional view taken along the line 4xe2x80x944 of FIG. 3.
The insulating material is made up of two halves only one of which is shown and which is indicated generally by the reference numeral 21. Basically it has a configuration complimentary to the armature core. This is comprised of a central portion 22 that has an opening 23 for passing the shaft of the associated armature. Radially extending teeth 24, which are complimentary to the armature teeth, extend outwardly and have a generally U-shaped configuration as shown in the cross sectional views of FIGS. 2 and 4. Generally the insulator 21 is quite thin, having a thickness of only about 0.5 mm.
This shape is comprised of individual side portions 25 that face the sides of the armature teeth and which are joined by an integral bridging portion 26 that extends generally in an axial direction relative to the axis of rotation of the machine. As a result, curved edge portions 27 result which are actually thinner than the thickness of the portions 25 and 26 and may be damaged due to the high pressure and loading occurring during the winding operation. If this insulator becomes damaged, then breaking may occur during the winding operation to damage the efficiency of the machine.
It is, therefore, a principal object to this invention to provide an improved insulator arrangement for the armature of a rotating electrical machine wherein the strength of the insulator is increased with significantly increasing its size or weight.
This invention is adapted to be embodied in a rotating electrical machine comprised of an armature having a circular core of a magnetic material and a plurality of magnetic pole teeth extending radially from the circular core for cooperation with a plurality of circumferentially spaced permanent magnets. Each of the magnetic pole teeth defines a core of generally rectangular cross section with slots formed between circumferentially adjacent pole teeth. An insulator having channel shaped portions covers at least in part the cores of the magnetic pole teeth. The channel shaped portions are comprised of radially extending slot portions extending along the sides of the pole teeth facing the slots. The slot portions are integrally joined by an axial portion extending across an axial outermost side of the pole teeth. The axial portion of the insulator channel shaped portions have a thickness greater than that of the side portions to avoid thinning at the juncture therebetween. Coil windings are wound around the cores of the magnetic pole teeth with the insulator being interposed therebetween.